1. Field of Invention
This invention relates generally to a module for producing a stream of hot and humid air, and more particularly to a module of this type adapted to operate in conjunction either with a proofing chamber in which dough pieces are raised prior to baking, or to operate in conjunction with a holding chamber in which cooked food is maintained in a hot and moist state suitable for serving, and to a module having a removable water pan with integrated electrical connection, and so a module having a humidity control.
2. The State of the Art
Proofing refers to a process by which pieces of yeast dough shaped to form bakery products are raised or enlarged preparatory to their being baked. Thus pastries, rolls, breads and other bakery products must undergo proofing before being put in an oven to be baked. When dough intermixed with live yeast is placed in a warm, moist environment, carbon dioxide is then internally generated throughout the body of the dough to create myriad gas pockets. These gas pockets enlarge or raise the dough and also alter its texture.
When the proofed dough is baked, the resultant product is lighter and more chewy than dough products which are not raised prior to baking. Thus croissants, doughnuts, pan pizzas, rolls and breads must be properly proofed before being baked. Proofing therefore is the process by which the shaped yeast dough pieces are subjected to a moist, hot-air environment to raise the pieces, and a proofing cabinet is a chamber in which proofing takes place.
It is vital that the atmosphere in which proofing takes place within a cabinet be properly controlled to avoid underproofing or overproofing. Thus should the dough pieces receive excessive heat, they will rise too fast, thereby producing large gas pockets that cause the pieces to collapse during baking. On the other hand, insufficient heat results in dough pieces that are not fully raised, and when these pieces are baked they will have a doughy core. Excessive moisture in proofing causes the product to have a mushy surface, while insufficient moisture renders the surface of the baked product tough and rubbery.
A module of the type disclosed in our above-identified copending application is highly effective in supplying a stream of hot, humid air to a proofing chamber in which the dough pieces in the chamber must be raised prior to baking.
But there is also a need for a stream of hot, humid air to be fed into a holding chamber. This chamber is similar to a proofing chamber, but it acts to maintain food that had already been cooked or baked in a hot and moist state until such time as the food must be served.
Thus in the dining halls of a large hotel at a convention attended by hundreds of guests, it is there necessary to serve dinner to all of these guests at a single sitting. However, as a practical matter it is not possible to provide kitchen facilities large enough to prepare these meals all at about the same time and to then serve these hot meals to the assembled guests.
In order to overcome this problem, the present practice in a hotel or other facility that has dining accommodations capable of serving a considerable number of guests is to prepare well in advance of the scheduled serving period, the required number of hot dinner plates. For example, if it is necessary to serve at a single sitting in a hotel dining hall five hundred hot plates, and the kitchen facilities of this hotel has a maximum cooking capacity of fifty hot plates, then several hours before the scheduled dining period, all five hundred hot plates are prepared in successive sessions.
In order to maintain these prepared hot food plates for several hours in a hot and moist condition suitable for serving, use is made for this purpose of holding cabinets. A holding cabinet is similar to a proofing cabinet in that it includes racks or shelves to support the pans, dishes or plates carrying the hot food. But while both in a proofing cabinet and in a holding cabinet, the atmosphere must be hot and humid, in a holding cabinet the necessary temperature is higher. Typically, in a proofing operation, the desired temperature level is about 80.degree. F. to about 130.degree. F., while the required relative humidity can be as low as about 70 percent or as high as about 95 percent. In a holding operation, the necessary temperatures to hold the cooked food at a temperature level suitable for serving is in a range of about 140.degree. F. to about 180.degree. F., and the relative humidity is in the range of about 20 to 90 percent.
In both a proofing and a holding operation it is essential that the relative humidity of the atmosphere be adjustable to satisfy the existing requirements for the dough or the cooked food being processed. This requirement is more difficult to meet in a holding cabinet in which the hot food being held therein dictates for the purpose a higher air temperature than in a proofing operation, yet a relative humidity that will maintain the moisture of the cooked food. Where the cooked food is say fried chicken that is somewhat dry, then the required relative humidity of the holding atmosphere is low, but if the cooked food is broiled fish, then a higher relative humidity is needed to maintain the fish in a moist state.
The relationship of air temperature to its relative humidity plays a significant role in the operation of a module for producing a stream of hot, humid air. It is important therefore that this relationship be understood. The "absolute humidity" is the weight of water in a pound of dry gas (the gas being air for the present purposes). When the partial pressure of water vapor in the gas reaches the vapor pressure of water at the same temperature, the air is saturated ("saturation humidity"). "Relative humidity" H (or "percent relative humidity") is the ratio, in percent, of the partial pressure of water to the vapor pressure of water at that temperature; i.e., the percentage of moisture actually in the air (its absolute humidity) to the moisture it would hold if it were saturated at the same air temperature and pressure. This saturation point, which represents the capacity of air to hold water vapor, increases as the temperature of air rises. Thus cold air, though it usually has a low moisture content, can have a high relative humidity with only a relatively small amount of water, for this cold air is almost saturated with respect to the maximum amount of water vapor it is capable of holding at such a cold temperature. But when the air is at a high temperature, it must then have relatively a very high moisture content to exhibit a high relative humidity.
If, therefore, in a module to produce a stream of hot and humid air one injects steam into a hot air stream to render it humid, the resultant percentage of relative humidity depends on the temperature of the air. For a given weight of injected steam, the relative humidity will be low if the temperature is elevated and will be higher if the temperature is lower.
In a module of the type disclosed in my prior U.S. Pat. No. 5,802,963 entitled "Module for Producing Hot Humid Air" 1 water from a replenishable reservoir is fed into a steam generator having an electric heater. Steam from this generator is injected into a duct in which an air blower draws in air through the inlet to the duct and blows it through an air heater to produce a humid, hot air stream which is exhausted from the outlet of the duct. The relative humidity of this stream depends on the amount of steam injected therein and the temperature of the air. Though with this module it is possible to adjust the temperature of the air stream as well as its relative humidity, we have found that it is not possible when operating in conjunction with a holding chamber to provide an atmosphere for this chamber that is appropriate for certain food holding conditions, such as an atmosphere whose air temperature is well above 130.degree. F. and whose relative humidity exceeds 50 percent.
As previously noted, more water vapor is required to produce a high relative humidity at higher temperatures. Thus if the air temperature is 130.degree. F. and a certain amount of steam is injected into the heated air to impart a high relative humidity thereto, for the same amount of steam and an air temperature of 150.degree. F. the relative humidity will then be substantially lower. The difficulty with the module disclosed in my prior patent is that it is unable to supply to the hot air stream whose air is at an elevated temperature the amount of steam needed to produce a high relative humidity. Hence the module, though capable of providing an atmosphere that is appropriate for wide range of conditions encountered in proofing, cannot provide an atmosphere that is appropriate for a wide range of holding conditions.